Cold Oil Temp?!?!?!

[Charles Schefer]

My "new" (to me) PA-30 recently came out of an extensive annual at Heritage Aero where Cliff Wilewski and his team did an outstanding job. This past weekend was the first time I've really had to fly her and give her some exercise since bringing her home 2 weeks ago. The flight was primarily to do some testing of the autopilot and so I was cruising around at 4,500MSL using power settings of 2,400 RPM and MP between 20"-23". Mixture was leaned to 9 GPH / side on the factory gauge (which was just overhauled during the annual by Air Parts of Lockhaven). The OAT was +3F. The climb out was 2500 RPM / 25" cowl flaps open. Cruising around cowl flaps went closed.

During the whole flight CHTs were perfect - around 300-320F, The odd thing was that the oil temp on both engines stayed fairly cool (bottom of the green even borderline yellow on the low temp side) which would (according to the factory gauge) be in the neighborhood of 60-80F. In concert with this the oil pressure stayed on the high-side. Still in the green but fairly high on the scale borderline yellow on the high side. Cooler thicker oil would indeed result in higher pressure but it's hard to believe that the oil was really only 60-80F the whole time. The vernatherms shouldn't even open until the oil gets to 160-180F (I would think).

To be clear I am talking about the factory original gauges which are all fairly fresh looking (the previous owner had almost all the instruments overhauled in the past 4 years). A JPI or Insight engine monitor is "on my list" but for now the factory gauges are what I have to work with.

I did some searches of the fourms for oil temps and found lots of people reporting high temps but not so much low temps. I did see some comments on low temps and the solution of putting metal duct tape (aka 200mph tape) partially over the oil coolers. I am not willing to do that I am not yet convinced the gauges are accurate. The fact that both engines are saying the exact same thing leads me to believe either - it is a voltage feedback issue to the guages or the temps really are quite cool (hence also high pressure) but again 60-80F is just not believable. Perhaps a bigger concern for me is if the guages are reading much lower than reality - come summer how do I know I am not over temping...

The ultimate solution is a proper engine monitor but regardless I do want anything in the aircraft to work properly (inc the factory guages). I am not convinced they are accurate but I also don't assume they are not...

I spoke to Cliff about all this and he agreed it seems odd and is chewing on it... any thoughts or feedback from the ICS would be greatly appreciated.

- Charles

[N3322G]

Where did the oil temp gauges sit before the annual? How long did you fly? Used to fly in Chicago temps like that and ran at 24/2400 at 4500 so that the engines would be hot enough to burn off bad stuff. I like to run closer to 400 CHT for that reason.

Any chance a ground got loose? since both gauges are doing the same thing, I'm inclined to guess it is the gauge rather than the engines but could be surprised there.

BTW, the reason I bought a JPI was I wanted to make sure the money I spent on O/H both engines was protected through good operations and for that, I needed data. I also bough the extra oil temp probe and kept the old Piper gauges as a double check.

[Charles Schefer]

[Zach Grant L1011jock]

Water boils at 212F. You can calebrate the gauge based on that, then you know how accurate it is.
-Zach

[md11flyer]

Charles,
Do you have the quick drain valves? If you do, after shutting down drain some oil over a turkey thermometer, should give a good
indication.

Gary

[Charles Schefer]

Zach / Gary - both great points / ideas thanks. I don't currently have quick drains but they are on my list to be added at the first oil change.

- Charles

[MULEFLY]

I would think that you can get a quick verification on the temperature of the dipstick immediately upon shutdown.... if it is hotter than 70F... you have false readings. Cliff does my work too... so I am based in a non-southern climate. I use a simple system to pump dry air in thru the oil tube during storage... when I get the airplane in the hanger and remove the dipsticks... they are definitely "hot"... another idea how warm is the oil filter?... can you keep your hand on it after shutdown...that would be another clue.

I saw your airplane at Cliff's it is VERY NICE ... hope the transmission for the gear is performing perfectly for you too!

All the best!
Jim

[Charles Schefer]

[Charles Schefer]

Follow-up on this topic. Attached is a pic of what my factory gauges look like in cruise at 8,000MSL on an almost perfect standard day (literally 15c and 29.93in-Hg when I took off and at 8,000MSL it was -1c):

I have a good digital multimeter which takes K-type temp probe input so I ordered a 19" long immersion temp probe from Meter-Depot.com to create this set-up:

I tested my new temp probe by putting it in freezing water and it read 32F. In boiling water it read 209-210F just a few degrees less than the 212F water boiling point. Thus for my purposes I think the temp probe is pretty accurate.

As you can see from the engine gauges in cruise the oil temps look low esp on the left side and also on the left side the oil pressure looks a tad on the high side.

When I landed and shut down I pulled the dip-sticks (within 5min of shut down) and put my temp probe down the filler tube to get an oil temp reading in the oil sump. The left sump was at 170F and the right sump which was 168F (both about where I believe they should be). I realize the temp in the sump is not going to be exactly the temp in the engine block or where the oil temp probe reads, but from this test I think I am dealing with a gauge issue and not actual low oil temp.

My next steps are to Ohm out the wires from the gauges to the back of the instrument cluster, check the grounds and also check the probes. If those all check out I may need to have the gauges calibrated.

Any thoughts, other ideas, or feedback appreciated...

- Charles

[N3322G]

Air Parts of Lock Haven re-calibrates these gauges when they O/H.

IIRC they said there is something special about removing these but it was 9 years ago and I've forgotten.

I use these gauges sort of lie idiot lights - if they are pegged one way of the other i worry but otherwise, I rely on the JPI etc.

[Charles Schefer]

[N3322G]

Don't know Insight - am VERY happy with JPI single-holer for twin. The problem determination alone has paid for itself.

Be sure to get the 5050A CHT probe for #3 so it can piggy back. #3 will run about 20-30 degrees cooler because of the add'l resistance but FAA regs say CHT has to be displayed at all times for cowl flap equipped aircraft so this is the cheapest way to comply.

[Charles Schefer]

[MULEFLY]

Yes Charles... they are the piggyback style. Perhaps it is because Pat took her airplane to Loch Haven... and had Airparts calibrate the system, that hers works. I have the piggyback probe set up and mine do not... the factory gauges barely move and the JPI probes are both showing the #3s as being about 30F cooler.

All the best!
Jim

[Charles Schefer]